Mission
The Tethered Aerostat Radar System, or TARS, is an aerostat-borne, surveillance program. Using the aerostat as a stationary airborne platform for a surveillance radar, the system is capable of detecting low altitude aircraft at the radar's maximum range by mitigating curvature of the earth and terrain masking limitations. TARS provides a detection and monitoring capability along the United States-Mexico border, the Florida Straits, and a portion of the Caribbean in support of the Department of Defense Counterdrug Program.

The primary agencies using the TARS surveillance data include U.S. Northern Command in support of Customs and Border Protection (Air and Marine Operations Center and Caribbean Air and Marine Operations Center) and U.S. Southern Command in support of Joint Interagency Task Force-South. In addition to its counterdrug mission, TARS surveillance data also supports North American Aerospace Defense Command's air sovereignty mission for the continental United States.

Features TARS consists of four major parts: the aerostat and airborne support equipment; the radar payload; the tether and winch system; and the ground station.

The aerostat used on the TARS program is a large fabric envelope filled with helium and air. The hull of the aerostat contains two chambers separated by a gas tight fabric partition. The upper chamber is filled with helium, a lighter-than-air gas, which provides the aerostat its lifting capability. The lower chamber is a pressurized air compartment (air ballonet). The aerostat hull is constructed of a lightweight, Tedlar fabric that weighs only eight ounces per yard. The fabric is resistant to environmental degradation, minimizes helium leakage, and provides structural strength to the aerostat. There is also a pressurized windscreen compartment underneath the aerostat that contains and protects the radar. A sophisticated system of sensors, blowers and valves controls the air pressure within the air ballonet, maintaining the aerostat's aerodynamic shape.

The TARS program uses two different sizes of aerostats, categorized by volume. The 275,000 cubic foot, or 275K, aerostat is 186 feet long and 62.5 feet in diameter with a fin span of 68.6 feet. The 420,000 cubic foot, or 420K, aerostat is 208.5 feet long and 69.5 feet in diameter with a fin span of 75.5 feet. These aerostats can rise up to 15,000 feet mean sea level, while tethered by a single nylon and polyethylene constructed cable. The normal operating altitude varies by site, but the norm is approximately 12,000 feet MSL. Aerostat power is developed by an on-board, 400 Hertz generator. The aerostat also carries a 100-gallon diesel fuel tank. All systems, to include the generator are controlled via an aerostat telemetry link.

The TARS program currently uses a Lockheed Martin, L-88A or L-88(V)3 radar. All radar data is transmitted to the ground station then digitized and fed to the various control centers for display. . The ground station is where a flight director, seated before banks of meters and television screens, monitors the aerostat's performance. A doppler weather radar, wind profiler and ground weather station are installed at each site to support flight operations. Each site also obtains up-to-date forecasts and weather warnings from the Air Force Weather Agency.

Operators launch the aerostat from a large circular launch pad containing a mooring system (fixed or mobile), depending on the site configuration. The mooring system contains a large winch with 25,000 feet of tether cable. During the launch sequence, the winch reels out the tether until the aerostat reaches operational altitude. When the aerostat is lowered, it is secured to a mooring tower. While moored, the aerostat weather vanes with the wind.

Background
The first aerostat were assigned to the Air Force in December 1980 at Cudjoe Key, Fla., with the original 250,000-cubic foot aerostat. An additional site was constructed and operated by the Air Force at Cape Canaveral, Fla., in 1983. This site was deactivated a few years later. During the 1980s, the U.S. Customs Service operated a network of aerostats to help counter illegal drug trafficking.

Their first site was built at High Rock, Grand Bahamas Island, in 1984. The second site was built at Fort Huachuca, Ariz., in 1986. Before 1992, three agencies operated the TARS network: the Air Force, U.S. Customs Service and U.S. Coast Guard. Congressional language in 1992 transferred management of the system to the Defense Department, with the Air Force as executive agent.

For security and safety reasons, air space around Air Force aerostat sites is restricted for a radius of at least two to three statute miles and an altitude up to 15,000 feet. This action saved the U.S. government several million dollars in annual operations and maintenance costs.

The operational sites are located at Yuma and Fort Huachuca, Ariz.; Deming, N.M.; Marfa, Eagle Pass and Rio Grande City, Texas; Cudjoe Key, Fla.; and Lajas, Puerto Rico. The contract management office is located in Newport News, Va. and the logistics hub is located in El Paso, Texas.